Lithography techniques include processes in which, for example, a resist film formed from a resist material is formed on top of a substrate, the resist film is selectively exposed with irradiation such as a light, an electron beam or the like through a mask in which a predetermined pattern has been formed, and then a developing treatment is then conducted, thereby forming a resist pattern of the prescribed shape in the resist film. Resist materials in which the exposed portions change to become soluble in a developing liquid are termed positive materials, whereas resist materials in which the exposed portions change to become insoluble in the developing liquid are termed negative materials.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beams (EB), extreme ultraviolet radiation (EUV) and X-rays.
Resist materials are required to have lithography properties such as sensitivity to the aforementioned light source and resolution enough to reproduce patterns with very fine dimensions. As resist materials which fulfill the aforementioned requirements, there is used a chemically-amplified resist containing a base resin that displays changed alkali solubility under the action of the acid, and an acid generator that generates an acid upon exposure. For example, a chemically-amplified positive resist includes, as a base resin, a resin in which the alkali solubility increases by the action of an acid, and an acid generator, and when an acid is generated from the acid generator upon exposure in the formation of a resist pattern, the exposed portions are converted to an alkali-soluble state.
Until recently, polyhydroxystyrene (PHS) or the resins (PHS-based resins) in which the hydroxyl groups have been protected with acid dissociable, dissolution inhibiting groups, which exhibit a high degree of transparency relative to a KrF excimer laser (248 nm), and a resin (acrylate-based resin) containing a structural unit derived from a (meth)acrylate ester in which a portion of the carboxyl groups are substituted with acid dissociable, dissolution inhibiting groups, which exhibit a high degree of transparency relative to an ArF excimer laser (193 nm), have been used as the base resin of chemically-amplified resists (for example, see Patent Reference 1).
(Patent Reference 1)
Japanese Unexamined Patent Application, First Publication No. 2003-241385.